GADZOOKS! project at Super-Kamiokande
M.Ikeda (Kamioka ICRR, U.of Tokyo)for Super-K collaboration2015,6,9@WIN2015
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Contents• GADZOOKS! project• Supernova Relic Neutrino search• R&D status and Plan• Summary
• Identify n̄ep events by neutron tagging with Gadolinium in SK.
•Gadolinium has large neutron capture cross section and emit 8MeV gamma cascade.
γ
p
n
Gde+
8 MeVΔT~30μsVertices within 50cm
ne
GADZOOKS! project
Physics targets:(1) Supernova relic neutrino (SRN)(2) Improve pointing accuracy for
galactic supernova(3) Precursor of nearby supernova by
Si-burning neutrinos(4) Reduce proton decay background(5) Neutrino/anti-neutrino
discrimination(6) Reactor neutrinos
Capt
ures
on
Gd
Gd in Water
100%
80%
60%
40%
20%
0%0.0001% 0.001% 0.01% 0.1% 1%
0.1% Gd gives~90% efficiencyfor n captureIn Super-K this means ~100 tons of water solubleGd2(SO4)3
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Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!
Beacom & Vagins PRL.93, (2004) 171101
Supernova Relic Neutrino (SRN)
Beginning of the universe
NOW
1 billion years ago
10 billion years ago
S.Ando, Astrophys.J. 607, 20(2004)
Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 3
Neutrinos from past SNe
Supernova Relic Neutrino (SRN)
Beginning of the universe
NOW
1 billion years ago
10 billion years ago
S.Ando, Astrophys.J. 607, 20(2004)
Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 4
Neutrinos from past SNe
First goal is discovery of SRN
Search for SRN at Super-KSearch window for SRN at SK : From ~10MeV to ~30MeV
Now SRN search is limited by BG. We need BG reduction by the neutron tagging which can be achieved by GADZOOKS! 5
Evaluating Gadolinium’s Action on Detector Systems200 m3 tank with 240 PMTs
15m3 tank to dissolve Gd Gd water circulation system(purify water with Gd)
Transparency measurement(UDEAL)
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EGADS
One of main goals for EGADS is to study the Gd water quality with actual detector materials. Thus, the detector fully mimic Super-K detector.: SUS frame, PMT and PMT case, black sheets, etc.
Gd dissolving test has been performed since Oct.2014. (see next page)
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EGADS detector: Baby-Kamiokande
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The light left at 15 m in the 200m3 tank was ~75% for 0.2% Gd2(SO
4)
3 ,
which corresponds to ~92% of SK-IV pure water average.
Transparency of Gd water with PMTs
Where we are now?
• Now, we are summarizing the R&D results and making a proposal.
• A committee which was formed to review and evaluate the proposal has started the review.
• After the review of the committee, we will start collaboration wide discussion in this June.
• If the proposal is approved, more detailed plan will be made also with T2K members.
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Summary
• GADZOOKS! is a project to upgrade Super-K, so that SRN ν ̄e can be tagged by the delayed coincidence signal from a neutron capture of Gd.
• EGADS detector was build for R&D of Gd water purification system and check Gd effect to Super-K.
• EGADS has been keeping a good water quality with the target Gd concentration after PMT installation.
• Collaboration wide discussion to decide the Gd installation to Super-K will start in June (two weeks).
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Improvement for Proton decay
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Neutron multiplicity for
Pe+p0 MC
92.5%Zero n
Atmospheric n BG
Accompany many n
If one proton decay event is observed at Super-K after 10 yearsCurrent background level: 0.58 events/10 yearsBackground with neutron anti-tag: 0.098 events/10 years
Background probability will be decreased from 44% to 9%.
Supernova burst case
ne+p
n+e
ne+p
n+e
Improve pointing accuracy e.g. 4~5° 3°(90%C.L.) for 10kpc.
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By identifying ne+p events enhance n+e events in angular distribution.Also, it enables us to extract ne + nx spectrum.
W/O n-tag With n-tag
10 kpc supernova
tag eff. = 1.0tag eff. = 0.8tag eff. = 0.0
Num
ber o
f sup
erno
vae
Pointing accuracy (1000 simulations for 10kpc supernova)
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20-38 degrees 38-50 degrees 78-90 degrees
E (MeV)
SK combined 90% C.L. (SK4 is not included yet)
E (MeV)E (MeV)
ne e+
p
n (invisible)
Signal region42o
μ, π
Low angle events Isotropic region
n Nn
reconstructedangle near 90o
dataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelic
< 5.1 ev / yr / 22.5 ktons = < 2.7 /cm2/s (>16 MeV) (using LMA model spectrum (Ando et.al, 2005)
SRN upper limit from SK PRD 85, 052007 (2012)
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Effect of Star formation rate• Nakazato et al. ApJ 804 (2015) 75
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